1. Field of the Invention
The present invention relates to a damper and spring unit for a vehicle suspension, particularly for a MacPherson suspension, provided with a vehicle height adjustment device for adjusting, i.e. for changing in a controlled manner, the height of the body of the vehicle from the ground.
2. Description of the Related Art
It is known to use height adjustment devices of the above-mentioned type on vehicle suspensions. These devices are used for example on so-called SUVs (Sport Utility Vehicles), in order to position the vehicle body at a greater height from the ground when the vehicle is running off road and at a smaller height from the ground when the vehicle running on road, especially at high speed. These devices are also typically used on sport cars, whose height from the ground is normally reduced to ensure better driving conditions at high speed, in order to allow to lift the vehicle body from the ground during particular manoeuvres, for example to enter or leave areas delimited by steep ramps, as well as to allow to drive the vehicle on a snowy road or in any other driving conditions for which it is preferable to have a height from the ground greater than the normal one.
Italian patent application No. ITTO20100695 in the Applicant's name discloses a damper and spring unit for a MacPherson suspension, comprising a device for adjusting the height of the vehicle from the ground which is made as a hydraulic linear actuator and is interposed between a top end of the spring and the vehicle body to change in a controlled manner the distance between the top end of the spring and the vehicle body. More specifically, the device comprises a cylinder coupled to the vehicle body and a piston which is slidable along the longitudinal axis of the cylinder and rests on a top spring plate.
International patent application No. WO2012/156418, also in the Applicant's name, discloses a damper and spring unit for a MacPherson suspension with a device for adjusting the height of the vehicle from the ground that is made as a hydraulic linear actuator and is interposed between the damper and the spring to change in a controlled manner the linear position of the bottom end of the spring relative to the damper cylinder, and hence relative to the axis of the wheel. More specifically, the device comprises a cylinder coupled to the damper cylinder and a piston that is slidable along the longitudinal axis of the cylinder and rests on a bottom spring plate. An adjustment device of this type, that is to say of the type interposed between the damper cylinder (as part of the suspension which is drivingly connected to the wheel carrier) and a bottom end of the spring, has the advantage, with respect to the other known solution discussed above, that it does not increase the vertical size of the suspension, but the disadvantage that it increases the radial size in the bottom area of the damper and spring unit, in which area the available space is usually very small.